Piezo-electric translating device



Nov. 17, 1931. A. A. THOMAS PIEZO ELECTRIC TRANSLATING DEVICE OriginalFiled March '24,. 1925 INVENTOR Patented Nov. 17, 1931 UNITED STATESPATENT OFFICE I ADOLPH A. THOMAS, OF NEW YORK, N. Y., ASSIGNOR 'IO WIREDRADIO, IlSTC OF NE YORK, N. Y., A CORPORATION OF DELAWARE Irmzo-nrno'rnrc TRANSLATING DEVICE Original application filed March 24,1925, Serial No. 17,900. Divided and this application filed February 17,1928. Serial No. 254,998.

My invention relates to means and methods for receiving and transmittingvariable electric impulses by the use of so-called piezoelectriccrystals. The piezo-electric devices and systems of my invention areparticularly useful for translating feeble electric impulses intoaudible sound. For'this reason my invention finds special application inradio c1rcuits, although not limited to this field of utility.

It has been known for many years-s1nce about 1880-that certain crystals,when subjected to pressure in certain directions, become electrified;that is to say, they become a source of electric potential and produce a'flow of current when properlyconnected in circuit. The reverse of thisphenomenon has also been observed namely, when such a crystal issubjected to an electric strain, a change in the dimensions of thecrystal takes place. In other words, it undergoes a slight expansion orcontraction. Among substances exhibiting these peculiar properties, areor stals of turmaline, quartz, Rochelle salts, oracite, fluor-spar, andperhaps others. These crystals are known as piezo-electrlc crystals, andthe electricity they produce is called piezo-electricity, which meanselectricity caused by pressure.

In the present invention, I make use of the foregoing properties ofpiezo-electric crystals to produce novel devices and systems fortransmitting and receiving feeble electric currents or impulses ofvariable character and amplifying them sufiiciently' for acousticreproduction. In carrying out my invention, I employ suitablepiezo-electric crystals in the construction of telephone transmittersand receivers, radio loudspeakers, and generally in electric circuits inwhich a piezo-electric crystal is subjected to mechanical stresses toproduce electric oscillations, or is subjected to electric stresses tocontrol a working circuit of principles of my invention, so that thosetion;

skilled in the art may fully understand the same. In these drawings 7Fig. 1 is aside view, partly in section, of a telephone transmitterembodying my inven- Fig. 2 is a front view of Fig. 1, approximately onsection line 22; a

Fig. 3 is a side view of a modified form of telephone transmitter orreceiver having a piezo-electric crystal along an axis at right anglesto the plane of the diaphragm;

Fig. 4 is a front view of Fig. 3,'with the diaphragm omitted, forclearness; and

' Fig, 5 shows diagrammatically a radioreceivmg circuit containing apiezo-electric crystal for operating a microphone or other resistancedevice in the output circuit.

Before proceeding with a detailed description of the various embodimentsillustrated in the drawings, I want it understood that the figures arefor the most part merely diagrammatic, and have been made as simple andclear as possible. This is particularly true as regards therepresentation of a piezo-electrio crystal, which I have shown in aconventional form to indicate any kind or form of piezo-electric crystalsuitable for use in this inventon;

Referring to Figs. 1 and 2, a piezo-electric crystal K is firmlysupported in any practical way, as between a pair of spring plates 1mounted on a base 2. If desired, a bolt 3 or similar fastening membermay be used to hold the crystal rigidly clamped between the plates. Themember 3, if metal, should be insulated from the metal plates 1.The'crystal is so supported that at the back it rests or bears againstan upstanding rigid wall 4 firmly mounted on the base 2 by screws 5 orotherwise. The wall or abutment 4 is preferably adjustable on the baseby meansof elongated slots 6, through which the bolts 5 pass.

' On the wall 4 are mounted pins 7 which arry suitable conductingsprings 8 in contact? with the opposite ends of the crystal. The pins 7also act as binding posts for connecting wires 9, by which the crystalis connected in the desired circuit.

In front of crystal K is mounted n acoustic diaphragm 10 held in a framediagrammatically indicated by 11. To the center of the diaphragm issecured a pressure plate or disk 12 arranged to bear against theadjacent face of the crystal.

The operation of the device shown in Figs.

land 2 will be clearly understood Without further description. It isonly necessary to say that the vibrations of the diaphragm 10, due tosound waves impinging upon it, produce varying pressures in the crystalK and these pressures cause the crystal to generate electric currents,in accordance with the degree of pressure exerted at any particularmoment. The ends of the crystal K, which are in contact with the springs8, may be covered with tin foil or other conducting material, in orderto secure a good electrical contact between the crystal and the springs.It will be understood that the rear abutment 4 is sufliciently strongand rigid to. remain .immovable (or practically so) under the pressuresexerted on the crystal-by the disk'12 of the vibrating diaphragm. Bymaking the abutment 4 adjustable toward and from the diaphragm 10, it iseasy to secure the correct initial or normal contact pressure betweenthe diaphragm and the crystal.

Figs. 3 and 4 illustrate, more or less diagrammatically, an arrangementin which the crystal is mounted in a position at right angles to thatshown in Figs. 1 and 2. The crystal K of.Figs. 3 and 4 is firmly clampedbetween a pair of spring plates 13 mounted on a base 14. The supportingplates 13 are preferably ofi'set'at 15 to provide shoulders jorreceiving the bottom face of the crystal. The rear end of crystal Krests against an upstanding wall 16 mounted on the base 14 by screws 17or'in any other practical way. The wall' 16 forms an immovable abutmentfor the crystal. The forward end of crystal K is in contact with thecenter of an acoustic di hragm 18, which is properly mounted in a amediagrammatically indicated at 19.

The crystal K is included in circuit by means of conductors 20-, whichare attached to the conducting plates 13 in any convenient way. Theabutment 16, like the abutment 4 of Figs. 1 and 2, may be adjustablewith respect to the diaphragm 18, so as to secure the correct normalposition of the crystal K with respect to the diaphragm 18 and theabutment 16.

As the operation of the device asshown in Figs. 3 and 4 is similar tothat of Figs. 1 and 2, nothing further need be said on this point. Thedevice of Figs. 3 and 4 may be used as a receiver or as a transmitter.

In Fig. 5 I have diagrammatically shown a crystal K rigidly mounted atone end in a suitable support 21, which is held rigid. The opposite endof crystal K is in contact with the movable disk or diaphragm 22 of amicrophone M, which may be of any approved orm or structure. It will beunderstood that the microphone M is illustrated in a purely diagrammaticway and is intended to represent any suitable resistance device adaptedto be varied by varying pressures of the crystal K against the movablediaphragm 22. The microphone M is connected in a circuit 23, which has abattery B and a primary coil 24. The secondary coil 25 is intended torepresent a part of whatever mechanism is operated or controlled byvariable currents in circuit 23. This will be understood by thoseskilled in the art without further description. The crystal K isincluded in a circuit 26. For this purpose I may use a pair ofconducting plates 27 held in intimate electric contact with oppositefaces of the crystal, as diagrammatically indicated in Fig. 5. Thecircuit wires are attached to the conducting plates 27 in any practicalway. The circuit 26 is inductively or otherwise connected with adetectorcircuit 28, which receives electric oscillations from an antenna29.

As the operation of radio-receiving cir cuits is generally wellunderstood b radio engineers, I need only say, in spea ing of theoperation of Fig. 5, that the variable voltages induced in circuit 26 bythe receiving oscillations in circuit 28 subject crystal K to variableelectric strains or pressures, and consequently the crystal undergoesslight expansion and contraction in the direction of its longitudinalaxis. That is to say, the crystal moves toward and from the diaphragm 22of the microphone in a vibratory manner, according to the electricoscillations of the circuit 26. These mechanical move ments of thecrystal 22 vary the resistance of the microphone M and thereby producecurrent variations in the circuit 23, which is normally supplied withsubstantiall constant potential from the battery B. T e currentvariations in coil 24 induce corresponding variations in the secondarycoil 25, which may operate a loudspeaker or any other electrical device.The vibrations of crystal K produce variations in the resistanceof themicrophone M in such a way that the electrical effect of the crystalmovements is amplified in the circuit 23, and therefore in the coil 25.

When I speak of a piezo-electric crystal, both in the description and inthe claims, I do not necessarily mean a complete crystal, but I includeany part or section of a crystal that ma be found to be operative. Forinstance, a p ate, rod or bar may be out from a crystal and used inconstructing my invention. The dimensions of such a crystal section willdepend upon the kind and size of crystal used. Furthermore, thedirection of the most effective mechanical and electrical strain in thecrystal will vary with different kinds of crystals, so that the best wayof mounting the crystal is often a matter of ex erimentation, which mayreadily be carrie out by those skilled in the art. When I, therefore, incertain claims refer to opposite ends of the crystal being in contactwith movable members, I mean any two contact faces or points of thecrystal between which physical movements of the crystal will take place.

Although I have explained my invention by means of certain constructionsand ar rangements, I wish to be understood that I have done so merely byway of illustration, and not as a restriction or limitation of myinvention. It is obvious that the various novel features of my inventionmay be mechanically embodied in other ways and by other means thanherein set forth.

This application is a division of my copending case filed March 24,1925, Serial Number 17,900, and is filed because of an ofiicialrequirement of division which made it 2 impossible for the applicant topresent the following claims in his original case.

I claim as my invention:

1. The combination of a base, a air of spaced members supported on saidass, a

piezo-elec-tric element arranged between said members, and a thirdmember supported transversely between said pair of members and passing,through said element.

2. The combination of a base, a pair of spaced spring plates supportedon said base, a piezo-electric element arranged between said plates, anda bolt supported crosswise by said plates and passing through saidelement.

as ADOLPI-I A. THOMAS.

